Load indicating member, apparatus and method

ABSTRACT

A method of measuring the load in a member subjected to longitudinal stress, a load measuring device and a fastener tightening device using the method of measuring, a load indicating member and a load indicating fastener for use in conjunction with the method of measuring, a method of making the load indicating fastener, and a method of tightening the load indicating fastener. A preselected end of a pin is secured to a shank of a load indicating member, such as a load indicating fastener, in a manner such that the pin is unaffected by the elastic deformation of the shank in response to longitudinal stress. Coplanar first and second flat surfaces are formed, respectively, adjacent to the longitudinal ends of the pin and the shank furthest from the preselected end of the pin such as to provide reference surfaces for the measurement of the elongation of the shank in response to longitudinal stress.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of my copending applicationSer. No. 670,260, now allowed, filed Nov. 12, 1984.

BACKGROUND OF THE PRESENT INVENTION

The present invention relates to load indicating members and loadindicating fasteners and further relates to methods and apparatuses formaking and using load indicating members and load indicating fasteningmembers. More particularly, the present invention relates to a method ofmeasuring a load in the load indicating member, a load measuring deviceusing the method of measuring the load, a fastener tightening tool fortightening a load indicating fastener member using the method ofmeasuring, a load indicating member and a load indicating fastener foruse in conjunction with the method of measuring, a method of making theload indicating fastener, and a method of tightening the load indicatingfastener.

In many operations, it is desirable to determine the amount of loadexperienced by a longitudinally stressed member. This information isparticularly useful when the longitudinally stressed member is afastener since the measurement of the longitudinal stress provides averification of the existence of a proper joint.

A prior technique which has been used to indicate the amount oflongitudinal stress experienced by a fastener is to provide a loadindicating feature to the fastener itself. This may be done byinterconnecting one end of an elongated member to a portion of thefastener prior to the installation of the fastener. The elongated memberextends parallel to the fastener and is unaffected by the elasticdeformation of the fastener in response to longitudinal stress. The freeend of the elongated member therefore provides a reference forindicating the elongation of the fastener in response to thelongitudinal stress.

Typically, the elongated member is a pin received within an elongatedbore disposed longitudinally of the fastener and extended from the headof the fastener and partially through the shank of the fastener. One endof the pin is interconnected with the shank of the fastener at the baseof the bore by means, for example, of adhesives, threads, or aninterference fit.

The various prior load indicating members and load indicating fastenersdiffered greatly in structure as well as in the methods and apparatuseswith which they were used to provide an indication of the elongation ofthe load indicating member or fastener.

For example, in the U.S. Pat. No. 3,602,186 issued Aug. 31, 1971 toCharles H. Popenoe, a fastener of this type is taught wherein the freeend of the pin is disposed within a recess formed in the head of thefastener and is submerged in a dark fluid filling the recess. Atransparent or translucent window is set in the recess to seal againstleakage of the fluid and to provide a view of the free end of the pin.When the fastener is in an unstressed condition, the free end of the pinrests flush against the window. As the fastener is stressedlongitudinally, the pin moves away from the window, changing the colorwhich is seen through the window and, thereby, providing a visualindication of the elongation of the shank of the fastener. If thefastener later becomes loosened, the indicator window reverts to itsoriginal color, providing a visual warning of the loosened condition. Avariation of this load indicating fastener is taught by U.S. Pat. No.3,799,108 issued Mar. 26, 1974 to Jack E. Mosow.

In U.S. Pat. No. 2,413,797 issued Jan. 7, 1947 to Albert R. Stone, afastener of this type is taught wherein the free end of the pin isprovided with a head spaced a predetermined distance away from apreselected surface formed on the fastener. When the fastener istightened to a preselected longitudinal stress, such as to result in apredetermined amount of elongation, the head of the pin engages thepreselected surface of the fastener to provide an indication that thedesired elongation has been achieved.

In the similar fastener taught by U.S. Pat. No. 3,248,923 issued May 3,1966 to Richard H. Blakeley, the free end of the pin is provided with afirst predetermined surface which becomes coplanar with a secondpredetermined surface of the fastener when a preselected stress level isreached. The fastener is calibrated by first being tensionedlongitudinally to the desired stress level. Then, either the free endsurface of the pin and the adjacent end surface of the head of thefastener are ground simultaneously to become coplanar or, alternatively,the pin is pressed into a reduced diameter bore in the base of theelongated bore until the free end surface of the pin is flush with theadjacent end surface of the head of the fastener. In the unstressedcondition of the fastener, the free end of the pin protrudes above theend surface of the head of the fastener. A similar fastener is taught byGerman Patent-schrift No. 745,925 published Dec. 23, 1943.

In U.S. Pat. No. 3,812,758 issued May 28, 1974 to Robert B. Bessler, Jr.and U.S. Pat. No. 3,823,639 issued July 16, 1974 to Theodore Liber, across bar is formed at the free end of the pin which indicates theelongation of the shank of the fastener relative to the elongated pin bytorsional deflection.

While the above-referenced seven patents each teach an acceptablestructure for providing a visible indication that a preselected amountof elongation has occurred, none of these patents provides for anumerical measurement of the exact amount of elongation which hasoccurred and none provides for the achievement of different amounts ofpreselected elongation for alternative installations of the samefastener. Furthermore, none of these patents provides for remotemonitoring of the fasteners either during or after installation.

Still another load indicating member and load indicating fastener istaught by U.S. Pat. No. 2,503,141 issued Apr. 4, 1950 to Albert R.Stone. The fastener is modified by providing an extra threaded bossextending from the head of the fastener in the opposite direction thanthe shank. The free end of the pin is substantially flush with the endof the threaded boss in the unstressed condition. A load measuringdevice is threaded onto the threaded boss. A plunger reciprocatesrelative to the load measuring device and engages the free end of thepin. The load measuring device detects when the plunger has moved apredetermined amount relative to the end of the boss such as to indicatethat a preselected stress level has been reached. A similar fastener anda similar load measuring device are taught by U.S. Pat. No. 3,943,819issued Mar. 16, 1976 to Charles S. Charron.

Both Stone '141 and Charron require a substantial modification to thehead of the fastener which results in the load indicating fastenerprotruding further than an unmodified fastener. It is thereforenecessary to manufacture the load indicating fasteners independentlysince it is not practical to modify existing bolts to the configurationstaught by either of these patents. Furthermore, neither Stone norCharron provide inexpensive, quick, and accurate means for aligning theload measuring device with the load indicating member when a measurementis being taken.

Yet other load measuring devices, load indicating members, and loadindicating fasteners using pins or similar elongated members to indicatethe elongation of the load indicating member or fastener are disclosedin U.S. Pat. No. 2,600,029 issued June 10, 1952 to Albert R. Stone, U.S.Pat. No. 3,908,508 issued Sept. 30, 1975 to William J. Payne; U.S. Pat.No. 3,987,668 issued Oct. 26, 1976 to Charles H. Popenoe; and U.S. Pat.No. 4,114,428 issued Sept. 19, 1978 to Charles H. Popenoe.

While each of the various prior load indicating members, and loadmeasuring devices cited above provides its own load indicatingfasteners, advantages in terms of accuracy, ease of manufacture, or easeof reading, none combines all of these advantages in a single structure.For example, none provides a compact load indicating member which may berapidly and reliably interconnected and accurately aligned with a loadmeasuring device. None provides an accurate load indicating fastenerwhich may be rapidly and inexpensively manufactured from existingfasteners. None provides for the protection of an accurate loadindicating member from contamination after installation and betweenreadings. None provides a load measuring device providing an accuratecontinuous measurement of the elongation of a fastener duringinstallation. Finally, none provides a fastener tightening toolresponsive to a load indicating member to provide a precise automatictightening operation for a fastener.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a load indicating member and a loadindicating fastener, as well as methods and apparatuses for the use ofthe load indicating member and the load indicating fastener, whichcombine many of the advantages, heretofore only available separately indifferent load indicating members or fasteners, in a single member orfastener. The present invention further provides additional features andadvantages not previously available in load indicating members, loadindicating fasteners, load measuring devices, and tightening tools.

The load indicating member of the present invention includes a shanksubjected to elastic deformation when stressed longitudinally, a firstflat surface formed adjacent to one longitudinal end of the shank, anindicator pin secured to the shank at a location remote from the firstflat surface, and a second flat surface formed at the free end of theindicator pin, the second flat surface being substantially coplanar withthe first flat surface when the shank is unstressed. The second flatsurface provides a reference for the measurement of the elongation ofthe shank.

A flexible member may be interconnected with both the first and secondflat surfaces and extended therebetween such as to form a seal to avoidthe contamination of the first and second flat surfaces and to avoidcontamination of the region between the indicator pin and the shank ofthe fastener, which contamination might otherwise reduce the accuracy ofthe load indication provided by the load indicating member.Alternatively, a removable cover may be fitted across the first andsecond flat surfaces and interconnected with the load indicating memberto seal against contamination before installation of the load indicatingmember as well as between readings after installation of the loadindicating member.

The load indicating fastener of the present invention includes afastener main body and an indicator pin. The fastener main body has ahead formed at one end thereof, a tool engagement surface formed aboutthe perimeter of the head, a shank extending longitudinally from thehead, a first flat surface formed adjacent the tool engagement surface,and a first partial bore disposed through the first flat surface andextended partially into the shank. The indicator pin is disposed withinthe first partial bore and is interconnected with the shank at alocation adjacent the base of the first partial bore. The indicator pinincludes a second flat surface coplanar with the first flat surface, thesecond flat surface providing a reference for the measurement of theelongation of the shank of the fastener main body in response tolongitudinal stress.

The method of making a load indicating fastener according to the presentinvention includes the steps of forming a first partial bore through thehead and partially into the shank of a fastener main body andinterconnecting one end of an indicator pin to the fastener main body atthe base of the first partial bore in a manner such that the indicatorpin is unaffected by the elastic deformation of the shank. The free endof the indicator pin is provided with a first flat surface thatprotrudes no further than the head of the fastener main body and iscoplanar with a second flat surface formed on or in the head of thefastener main body.

The load measuring device according to the present invention provides aseat member selectively engagable with the first flat surface of theload indicating member, a probe movably interconnected with the seatmember and selectively engagable with the second flat surface, and adifferential displacement measurement device responsive to thedisplacement of the probe relative to the seat member such as to providean accurate measurement of the elongation of the shank relative to thepin when the shank is stressed longitudinally.

The load measuring device may be permanently installed in a recess inthe head of the load indicating member or, alternatively, may beremovably engaged with the load indicating member by cooperatingalignment features of the load measuring device and the load indicatingmember.

The output of the load measuring device may be used to provide acontinuous reading of the instaneous elongation of the fastener or,alternatively, may be used to determine when the fastening operation iscomplete or to provide an indication of the load in a previouslytightened fastener. When the load indicating member is a fastener, theload measuring device may be used simultaneously with a fastenertightening tool or, alternatively, may be incorporated directly into thefastener tightening tool. When the fastener tightening toolincorporating the load measuring device is of an automatic tighteningtype, the elongation indication in the load measuring device may becombined with other parameters, monitored by the fastener tighteningtool, such as angle and torque, to determine when the tightening cycleis complete and to detect irregularities in the joint.

The method of measuring the load in a load indicating member accordingto the present invention includes the steps of interconnecting a loadmeasuring device of the present invention with a load indicating memberof the present invention and measuring the elongation of the shank ofthe load indicating member relative to the indicating pin thereof.

The method of tightening a load indicating fastener according to thepresent invention includes the steps of interconnecting a load measuringdevice according to the present invention to the head of a loadindicating fastener according to the present invention, tightening theload indicating fastener while continuously monitoring the loadmeasuring device to determine when a preselected load is reached, andceasing the tightening of the load indicating fastener when thepreselected load is reached, as indicated by the load measuring device.

A primary object of the present invention is to provide an inexpensiveand accurate method of measuring the load in the load indicating member,a load indicating device and a fastener driving tool using the method ofmeasuring of the present invention, a load indicating member for use inconjunction with the method of measuring of the present invention, amethod of making the load indicating member of the present invention,and a method of tightening the load indicating fastener of the presentinvention.

Another object of the present invention is to provide an inexpensivemethod of making a reliable, accurate and compact load indicatingfastener from a conventional fastener.

Another object of the present invention is to provide a method and anapparatus for reliably and removably aligning a load measuring devicewith a load indicating member or fastener and for repeatedly orcontinuously monitoring the load indicating member or fastener.

Still another object of the present invention is to provide a loadindicating member or fastener of the indicator pin-type described abovewith a means for protecting the indicator pin and for protecting thefirst and second surfaces thereof from contamination.

Yet another object of the present invention is to provide a loadindicating fastener which may be tightened by conventional tighteningtools and, more particularly, to provide a load indicating fastenerwhich may be monitored by a load measuring device during a tighteningoperation.

Still another object of the present invention is to provide a method forproviding a continuous indication of the load in a load indicatingfastener during a tightening operation or during use of the device towhich the fastener is attached.

Still yet another object of the present invention is to provide afastener tightening device for use in conjunction with a load indicatingfastener, which fastener device provides an automatic fasteningoperation responsive to a measurement of the elongation of the shank ofthe load indicating fastener relative to an indicator pin during thetightening operation.

These and many other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art when thefollowing exemplary detailed description of the present invention isread in conjunction with the drawings appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference numerals refer to like elementsthroughout:

FIG. 1 depicts a load indicating member according to the presentinvention and, more particularly, illustrates a load indicating fastenerin an unstressed condition together with a removable protective cap;

FIG. 2 is a partially schematic sectional view illustrating the loadindicating fastener of FIG. 1 in an installed condition and furtherillustrating an example of a load measuring device engaged with the loadindicating fastener for measuring the load experienced thereby accordingto the present invention;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2;

FIG. 4 is a partially schematic sectional view illustrating a method bywhich the zero reading of the load measuring device of FIG. 2 may becalibrated;

FIG. 5 is a partially schematic sectional view illustrating an exampleof a load indicating member according to the present inventionincorporating a load measuring device in a recess formed therein;

FIG. 6 is a partially schematic sectional view, of an alternate exampleof a load indicating fastener and of a load measuring device, eachaccording to the present invention; and

FIG. 7 is a partially schematic sectional view of another alternateexample of a load indicating fastener and of a load measuring device,each according to the present invention; and

FIG. 8 is a partly cut-away partial side view depicting a loadindicating fastener according to the present invention as well as afastener tightening tool engaged therewith, the fastener tightening toolincorporating a load measuring device according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and more particularly to FIGS. 1 and 2thereof, a first example of a load indicating member, and moreparticularly, a load indicating fastener 10 is illustrated. The loadindicating fastener 10 is formed from a conventional bolt which has beenmodified to provide an indication of the elongation of the bolt during atightening operation as well as at various other times during the lifeof a joint. The bolt has a shank 12 (provided at one of its ends) withthreads 14 at one end and (at the other of its ends) with a head 16 atthe other end. A shoulder 18 is formed between the head 16 and the shank12. The head 16 has a generally flat upper surface 20 disposed normal tothe longitudinal axis 22 of the shank 12. The head is also provided witha wrenching or tool engagement surface 24, such as a hexagonal wrenchingsurface, disposed about the periphery thereof.

The bolt is modified to provide a load indicating fastener 10 asfollows:

A first bore 26 is provided extending along the longitudinal axis 22 ofthe bolt and extending from the upper surface 20 thereof partially intothe shank 12. A second bore 28 is axially aligned with the first bore 26and extends downwardly from the base of the first bore. A pin 30 isdisposed within the first bore 26. A first end 32 of the pin 30 ispressed into second bore 28 in a manner such as to interconnect the pin30 with the shank 12 of the load indicating fastener 10. A second end 34of the pin 30 is disposed adjacent the upper surface 20 of the head 16.It will be appreciated by those skilled in the art that the second end34 of the pin 30 will be unaffected by any elastic deformation of theshank 12 of the load indicating fastener 10 when the load indicatingfastener is longitudinally stressed.

The second end 34 of the pin 30 is provided with a flat upper surface 36which is coplanar with the upper surface 20 of the head 16. This may beaccomplished by pressing the pin 30 into the second bore 28, duringinstallation of the pin, until the upper surface 36 of the pin 30 isproperly aligned with the upper surface 20 of the head 16.Alternatively, the upper surface 36 of the pin 30 or the upper surface20 of the head 16, or both, may be ground after installation of the pinso as to be coplanar.

A protective cover 38 may be fitted onto the head 16 of the loadindicating fastener 10 in order to protect the upper surfaces 20 and 36from contamination and damage during transport, as well as to protectthese surfaces after the load indicating fastener has been installed.The protective cover 38 has a flange portion 40 removably engaging thetool engagement surface 24 of the head 16.

A load indicating fastener 10 may be very precisely manufactured so asto provide an accurate measurement, in the manner described below, ofthe elongation of the shank 12 by locating the base of the first bore 26a predetermined depth h below the shoulder 18 of the load indicatingfastener.

An example of a load measurement device 42 for use in conjunction withthe load indicating fastener 10 is depicted in FIGS. 2 and 3. The loadmeasurement device 42 includes a socket member 44 having an internalhead engagement surface 46 engagable with the tool engagement surface 24of the head 16 of the load indicating fastener 10. The socket member 44aligns the load measurement device 42 with the longitudinal axis 22 ofthe load indicating fastener 10. The socket member 44 is provided with abore 48 aligned with a longitudinal axis 22.

Adapter pad 50 is received in the bore 48 and secured in positiontherein by set screw 52. The adapter pad 50 is provided with a pluralityof bosses or legs 54, each of the legs 54 being engagable with the uppersurface 20 of the load indicating fastener 10, as illustrated in FIG. 2.Preferably, as illustrated in FIG. 3, there are three legs, 54a, 54b,and 54c disposed in an array about the longitudinal axis 22 to preciselyalign the adapter pad 50 with the longitudinal axis 22 of the loadindicating fastener 10.

As best shown in FIG. 2, the load indicating device 42 includes adifferential displacement measurement device 56 having a portiondisposed within a bore 60 in the adapter pad 50 and secured in positiontherein by means of a set screw 58. A probe 62 extends from thedifferential displacement measurement device 56 into engagement with theupper surface 36 of the pin 30. The differential displacementmeasurement device 56 is interconnected in a manner well known to theart by suitable wiring 66 to a display device 68 to provide anindication of the position of the probe 62. Various appropriatedifferential displacement measurement devices are well known in the artand, accordingly, the differential displacement measurement device 56 isnot shown or described in detail herein.

In use, the load indicating fastener 10 may be used to secure panels 70and 72 together by being passed progressively through suitable borestherein and the panels are fastened together by a threaded nut 74 and awasher 76. A suitable tightening tool, not illustrated, engages the toolengagement surface 24 of the load indicating fastener 10 and is rotatedto tighten the joint. As the panels 70 and 72 engage, respectively, theshoulder 18 and the washer 76, the shank 12 of the load indicatingfastener experiences longitudinal stress causing longitudinal elasticdeformation of the shank 12. Since the pin 30 is unaffected by thelongitudinal stress, the amount of elongation of the shank 12 can bemeasured by the load measurement device 42 by measuring the heightdifferential between the upper surfaces 20 and 36, respectively, of thehead 16 and the pin 30.

While FIG. 2 illustrates the use of the load measurement device 42 tomonitor the condition of the joint at various discrete times, such asbefore and after the joint is formed or at a predetermined period oftime after the joint has been formed, it should be recognized that theload measurement device may be used during the tightening process tocontinuously monitor the tightening process and, if desired, todetermine when the tightening function is complete. This may be done byproviding commutator means, not illustrated in FIG. 2 but well known inthe art, between the differential displacement measuring device 56 andthe wiring 66 so as to facilitate the rotation of the load measurementdevice 42 during the tightening operation. A handle, also not shown inthe drawing, may be interconnected by any suitable means with the socketmember 44 so as to provide leverage for the rotation of the socketmember and, thereby, to provide means for manually tightening the loadindicating fastener 10.

It should be noted that the design of the load indicating fastener 10described above facilitates rapid modification of existing bolts. Itfurther facilitates the rapid interconnection of conventionaldifferential displacement measuring device 56 therewith since theexisting tool engagement surface 24 and upper surface 20 of the bolt isused for interconnection and alignment of the differential displacementmeasuring device 56. The socket member 44 may be a conventional socketmember of the type used with a socket type tightening tool and,accordingly, only the adapter pad 50 needs to be specially manufacturedto act as an adapter between the socket member 44 and the differentialdisplacement measuring device 56.

The use of the load indicating fastener 10 and the load measurementdevice 42, according to the present invention, offers the advantage ofimproving the repeatability and the reliability of the measurementsobtained. Since the upper surfaces 20 and 36 are coplanar when the loadindicating fastener 10 is unstressed, there is no need to recalibratethe load measuring device 42 for each installation. Furthermore, itpermits the use of a load measurement devices 42 to detect changes in ajoint long after the installation has occurred without maintainingrecords as to how the joint was formed.

A load measurement device 42 according to the present invention may beeasily calibrated to provide a zero reading for an unloaded condition asshown in FIG. 4, by the use of a flat reference surface 78. The displaydevice 68 is adjusted in such a manner as to provide a zero reading whenthe legs 54 of the adapter pad 50 and the probe 62 engage the flatreference surface 78.

An alternate example of a load indicating fastener 10' made from aconventional bolt according to the present invention is illustrated inFIG. 5. The load indicating fastener 10' thereof is provided with alarge recess 80 formed in the head 16'. A recessed flat surface 82 isformed in the base of the recess 80, the recessed flat surface 82 beingnormal to the longitudinal axis 22 of the bolt. The pin 30' is suitablyinterconnected with the shank 12' at the base of a first bore 26'extending along the longitudinal axis 22 of the load indicating fastener10'. The upper surface 36' of the pin 30' is disposed in a manner suchas to be coplanar with the recessed flat surface 82 when the loadindicating fastener 10' is unstressed.

A load measurement device 42' disposed within the recess 80 includes aadapter pad 50' and an external engagement surface 46' engagable withthe inner wall of the recess 80. A plurality of legs 54' extenddownwardly from the adapter pad 50' into engagement with the recessedflat surface 82.

As shown schematically in FIG. 5, a compact differential displacementmeasuring device 56', well known in the art, is disposed within a recess60' formed in the adapter pad 50'. A probe 62' extends from thedifferential displacement measurement device 56' along a bore 84 in theadapter pad 50'. The free end of the probe 62' engages the upper surface36' of the pin 30'.

A protective cover 38' is fitted into the recess 80 and is suitablyinterconnected with the head 16' of the load indicating fastener 10' ina manner such as to secure the adapter pad 50' in the recess 80 andfurther such as to seal the recess 80 from contaminants. A displaydevice, not shown in the drawing, may be interconnected with thedifferential displacement measurement device 56' by suitable wiring 66'extending through an apperature 86 in the protective cover 38'.

The load indicating fastener 10' is more expensive to manufacture thanthe load indicating fastener 10 described previously. However, the loadindicating fastener 10' offers the advantage of being completelyself-contained except for the display device. The load indicatingfastener 10' has the additional advantage that, when a suitablecommutator is provided, the measurement of the elongation of the shank12' may be continuously monitored while the load indicating fastener 10'is being tightened by any conventional tightening tool which permitspassage of the wiring 66'. Thus, the tightening operation used in anyconventional tightening tool can be controlled or verified using theelongation information obtained from the differential displacementmeasurement device 56'.

Another variation of a load indicating fastener 10", according to thepresent invention, is illustrated in FIG. 6. A recess 80" is formed inthe head 16" of the load indicating fastener 10" to provide a recessedflat surface 82". The recessed flat surface 82 is coplanar, in theunstressed condition of the load indicating fastener 10", with the uppersurface 36" of a pin 30" interconnected with the load indicatingfastener 10" in the manner described previously.

In use, an adapter pad 50" is removably insertable in the recess 80".The adapter pad 50" is provided with an outer surface 88 engagable withthe recess 80" in a manner such as to axially align the adapter pad 50"with the pin 30". A differential displacement measurement device 56" isinterconnected with the adapter pad 50" by means of a set screw 52" andwith a display device 68" by means of suitable wiring 66" in a mannersimilar to that described above for the load measurement device 42.

Yet another example of a load indicating fastener 10'" is illustrated inFIG. 7. The load indicating fastener 10'" is provided with a firstrecess 90 and a second recess 92 formed in the head 16'" thereof. Thesecond recess 92 is shallower than the first recess 90 and alignedtherewith such as to define a shoulder 91 therebetween. A pin 30'" isprovided in a bore 26'" in a manner such that an upper surface 36'" isaligned with the shoulder 91. A flexible plate 94 is disposed within thesecond recess 92 and is interconnected about is perimeter with theshoulder 91. The flexible plate 94 also engages the upper surface 36'"of the pin 30'". The flexible plate 94 acts as a cover to protect theupper surface 36'" of the pin 30'", the shoulder 91, and the secondrecess 92 from contamination. A load measurement device 42 of the typedescribed above may be used in conjunction with the load indicatingfastener 10'" by engaging the legs 54 of the adapter pad 50 thereof withthe portion of the flexible plate 94 which is disposed above theshoulder 91 while engaging the probe 62 with the portion of the flexibleplate 94 which is engaged with the pin 30'".

FIG. 8 illustrates an example of a fastener tightening apparatus 100adaptable for use in conjunction with a load indicating fastener 10' aload indicating fastener 10", or a load indicating fastener 10'"according to the present invention. In the example of structureillustrated in the drawing, the fastener tightening apparatus 100 isdepicted installing a load indicating fastener 10.

The fastener tightening apparatus 100 includes a conventional powertool, only the housing 102 of which is shown in the drawing. Theconventional power tool has a rotary output driver 104 engagable with amodified socket member 44'". The modified socket member 44" has anengagement surface 46'" engagable with the head 16 of the loadindicating fastener 10. A differential displacement measurement device56 is disposed within a cavity 106 formed in the modified socket member44'". A plurality of legs 54'" extend from the modified socket member44'" into engagement with the upper surface 20 of the load indicatingfastener 10. The probe 62 of the differential displacement measurementdevice 56 extends through a suitable aperture 108 in the modified socketmember 44'" for engagement with the pin 30 of the load indicatingfastener 10. The housing 102 and the modified socket member 44'" areprovided, respectively, with cooperating commutation elements 110 and112 for electrically interconnecting the differential displacementmeasurement device 56 with the power tool.

It will be appreciated by those skilled in the art that the power toolmay be provided with a display device, not shown in the drawing, fordisplaying the measurement of elongation obtained during the fasteningoperation. Alternatively, the power tool may be adapted to use theinformation continuously supplied by the differential displacementmeasuring device 56 to determine when a predetermined amount ofelongation has occurred and when a tightening operation should bestopped.

It will further be appreciated by those skilled in the art that thepower tool chosen may, in a manner well known in the art, monitor othercharacteristics of the joint being formed, such as the torque and theinstantaneous angle of the load indicating fastener. An example of sucha power tool, may be found in U.S. Pat. No. 4,344,216 issued 8/17/82 toRobert J. Finkelston. This other information available from the powertool may be combined with the elongation information supplied by themodified socket member 44' to provide a precisely controlled tighteningoperation wherein the various measured parameters are each used directlyto control the tightening sequence or to monitor the results of thetightening operation. For example, the modified socket member 44' may beused in conjunction with the power tool using what is known in the artas a "turn of the nut" tightening sequence, while the elongationinformation is used subsequently to determine whether the joint formedby the tightening sequence meets certain specifications.

The fastener tightening apparatus 100 and the modified socket member 44'thereby facilitate rapid formation of reliable joints having repeatableand predictable characteristics. The fastener tightening apparatus 100and the modified socket member 44' also provide for a means to detectflaws in a joint during the actual installation process, thus reducingthe risk of a catastrophic joint failure.

The above detailed description includes the best mode for carrying outthe invention contemplated by the inventor at the time of filing of thepresent application. It will be appreciated by those skilled in the artthat many modifications may be made to the load indicating fastener, theload measurement device, and the fastener tightening apparatus describedabove without departing from the spirit of the present invention. Suchmodifications are included within the intended scope of the claimsappended hereto.

What is claimed as novel is as follows:
 1. A load indicating membercomprising:a shank, which, when stressed longitudinally, is subject toelastic deformation such that one portion thereof moves relative toanother portion thereof; a recess formed adjacent one longitudinal endof said shank; a first flat surface formed in the base of said recess;an indicator pin having one longitudinal end disposed adjacent saidfirst flat surface and an other longitudinal end disposed remotetherefrom, said other longitudinal end being secured to said shank at alocation remote from said first flat surface, said pin being unaffectedby said elastic deformation of said shank; and a second flat surfaceformed at said one longitudinal end of said pin, said second flatsurface being substantially parallel with said first flat surface whensaid shank is unstressed, said second flat surface providing a referencefor measurement of the elongation of said shank.
 2. The load indicatingmember of claim 1 further comprising:a head formed integrally with saidshank at said one longitudinal end thereof adjacent said first flatsurface said recess being formed in said head; fastening means formedintegrally with said shaft at the other longitudinal end thereof remotefrom said first flat surface; a first bore extending longitudinally ofsaid shank and partially through said shank and having an open enddisposed adjacent said first flat surface and a base end disposed remotetherefrom, said indicator pin being disposed within said first bore; anda second bore having a smaller diameter than said first bore, saidsecond bore extending longitudinally of said shank partially throughsaid shank from said base end of said first bore to a location remotetherefrom said indicator pin being interconnected with said shank byhaving one end thereof secured in said second bore.
 3. The loadindicating member of claim 1 wherein said recess is formed at said firstlongitudinal end of said shank.
 4. The load indicating member of claim 1further comprising:a load measuring device disposed within said recess,said load measuring device having portions respectively engaging saidfirst flat surface and said second flat surface and being responsive tothe elongation of said shank relative to said indicator pin such as toprovide a measurement of the elongation of said shank.
 5. The loadindicating member of claim 1 further comprising:engagement means formedat said one longitudinal end of said shank for removably positioning aload measuring device relative to said first and second flat surfacessuch as to provide a measurement of the elongation of said shank.
 6. Theload indicating member of claim 5 wherein said engagement meanscomprises the surfaces of said recess formed in said shank.
 7. The loadindicating member of claim 5 further comprising:cap means removablyengagable with said engagement means to protect said load indicatingmember from debris and contaminants.
 8. The load indicating member ofclaim 1 further comprising:a head formed integrally with said shank atsaid one longitudinal end thereof, said recessed being formed in saidhead; and engagement means formed on said head for positioning a loadmeasuring device relative to said first and second flat surface such asto provide a measurement of the elongation of said shaft.
 9. The loadindicating member of claim 1 further comprising:cap means removablyengagable with said elongated shank to close said recess such as toprotect said load indicating member from debris and contaminants.
 10. Aload measuring device for use in conjunction with a load indicatingmember having a shank, a first flat surface formed adjacent to onelongitudinal end of said shank, first engagement means formed at saidone longitudinal end of said shank, a pin secured to said shank at alocation remote from said first flat surface, and a second flat surfaceformed on said pin and disposed parallel to said first flat surface,said load measuring device comprising:adapter means selectivelyengagable with said first flat surface; probe means movablyinterconnected with said adapter means, said probe means beingselectively engagable with said second flat surface; second engagementmeans selectively engagable with said first engagement means when saidload measuring device is used in conjunction with said load indicatingmember such as to axially position said probe means relative to saidpin; and measurement means responsive to the displacement of said probemeans relative to said adapter means such that said measurement meansprovides a measurement of the elongation of said shank relative to saidpin when said shank is stressed longitudinally.
 11. The load measuringdevice in claim 10 wherein said first flat surface is disposed adjacentone end of said shank and further wherein said pin is disposed in apartial bore passing through said first flat surface, said loadmeasuring device further comprising:recess means formed in said adaptermeans, said probe means being reciprocably disposed in said recess meanssuch as to be reciprocable relative to said seat means toward and awayfrom said second flat surface; and feet means extending from saidadapter means for engagement with said first flat surface, said feetmeans being disposed in an array about said recess means such as toposition said adapter means on said first flat surface in a mannerplacing said probe means in axial alignment with said pin.
 12. The loadmeasuring device of claim 10, wherein said load indicating membercomprises a fastener having a head formed at said one end of said shank,and said first engagement means comprises tool engagement means formedon said head; and further wherein:said second engagement means of saidload measuring device further comprises tool means selectively engagablewith said tool engagement means such that said fastener is selectivelyrotated by rotation of said tool means.
 13. The load measuring device ofclaim 12 further comprising:interconnection means for interconnectingsaid tool means with wrenching means such as selectively impart arotational motion to said fastener to install and to remove saidfastener while measuring the elongation thereof.
 14. The load measuringdevice of claim 13 wherein said measurement means provides an outputsignal indicative of the elongation of said shank and further whereinsaid load measuring device further comprises:commutator means forcommunicating said output signal to said wrenching means.
 15. The loadmeasuring device of claim 10 wherein said first engagement meanscomprises a recess formed in said shank and said second engagement meanscomprises a portion of said load measurement device engagable with saidrecess, said first flat surface being disposed at the base of saidrecess.
 16. A method of tightening a load indicating fastener of thetype having a shank subject to elastic deformation when stressedlongitudinally, a head formed at one longitudinal end of said loadindicating fastner, a first flat surface formed adjacent said head, toolengagement means formed on said head adjacent said first flat surface,an indicator pin having one longitudinal end disposed adjacent saidfirst flat surface and an other longitudinal end secured to said shankat a location remote from said head, and a second flat surface formed atsaid one longitudinal end of said pin, said method comprising the stepsof:simultaneously engaging a tightening tool with said tool engagementmeans, engaging adapter means with said first flat surface, and engagingprobe means with said second flat surface said adapter means beingfixedly interconnected with said tightening tool and said probe meansbeing reciprocally interconnected with said adapter means; operatingsaid tightening tool to tighten said load indicating fastener; andmeasuring the displacement of said probe means relative to said adaptermeans such as to provide a continuous measurement of the elongation ofsaid shank during the operation of said tightening tool.
 17. The methodof claim 16 wherein said step of operating said tightening tool furthercomprises rotating said tightening tool until the occurence of acondition measured by said tightening tool indicative of a proper joint,said method further comprising the step of:verifying the existence of aproper joint using the measurement of the displacement of said probemeans relative to said adapter means.
 18. The method of claim 16 furthercomprising the step of:ceasing operation of said tightening tool whensaid measuring step indicates that a predetermined amount of shankelongation has occurred.
 19. A method of measuring the load indicatingfastener of the type having a shank subject to elastic deformation whenstressed longitudinally, a head formed at one longitudinal end of saidload indicating fastener, a first flat surface formed adjacent saidhead, tool engagement means formed on said head adjacent said first flatsurface, an indicator pin having one longitudinal end disposed adjacentsaid first flat surface and an other longitudinal end secured to saidshank at a location remote from said head, and a second flat surfaceformed at said one longitudinal end of said pin, said method comprisingthe steps of:engaging socket means with said tool engagement means, saidsocket means further comprising leg means engagable with said first flatsurface and probe means reciprocably interconnected with said leg meansand engagable with said second flat surface; and measuring the positionof said probe means relative to said leg means.
 20. An adapter for aload measuring device for use in conjunction with a load indicatingmember having a shank, a first flat surface formed adjacent onelongitudinal end of said shank, a pin secured to said shank at alocation remote from said first flat surface, and a second flat surfaceformed on said pin and disposed parallel to said first flat surface,said adapter means comprising:a main body; a bore extending through saidmain body, said bore being adapted to reciprocally receive probe meanstherein; interconnection means adapted to interconnect said main bodywith measurement means responsive to displacement of said probe meansrelative to said mainbody; and feet means extending from said main bodyfor engagement with said first flat surface, said feet means beingdisposed in an array about said recess means such as to position saidadapter means on said first flat surface in a manner placing said borein axial alignment with said pin; and further such that, uponinterconnection of said measurement means with said main body, andengagement of said probe means with said first flat surface, saidmeasurement means provides a measurement of the elongation of said shankrelative to said pin when said shank is stressed longitudinally.
 21. Theadapter of claim 20 wherein said load indicating member furthercomprises first engagement means formed at one end of said shank, saidadapter further comprising:second engagement means selectively engagablewith said first engagement means when said adapter is used inconjunction with said load indicating member such as to axially positionsaid probe means relative to said pin.
 22. The adapter of claim 20wherein said load indicating member comprises a fastener having a headformed at said one end of said shank, and said first engagement meanscomprises tool engagement means formed on said head; and furtherwherein:said second engagement means of said load measuring devicefurther comprises tool means selectively engagable with said toolengagement means such that said fastener is selectively rotated byrotation of said tool means.
 23. The adapter of claim 22 furthercomprising:interconnection means for interconnecting said tool meanswith wrenching means such as selectively impart a rotational motion tosaid fastener to install and to remove said fastener while measuring theelongation thereof.
 24. The adapter of claim 23 wherein said measurementmeans provides an output signal indicative of the elongation of saidshank and further wherein said load measuring device furthercomprises:commutator means for communicating said output signal to saidwrenching means.
 25. An installation tool for installing a loadindicating fastener of the type having a shank, a first flat surfaceformed adjacent to one longitudinal end of said shank, tool engagementmeans formed at said shank, a pin secured to said shank at a locationremote from said first flat surface, and a second flat surface formed onsaid pin and disposed parallel to said first flat surface, saidinstallation tool comprising:adapter means selectively engagable withsaid first flat surface; probe means movably interconnected with saidadapter means, said probe means being selectively engagable with saidsecond flat surface; second engagement means selectively engagable withsaid first engagement means when said load measuring device is used inconjunction with said load indicating member such as to axially positionsaid probe means relative to said pin; and measurement means responsiveto the displacement of said probe means relative to said adapter meanssuch that said measurement means provides a measurement of theelongation of said shank relative to said pin when said shank isstressed longitudinally, tool means selectively engagable with said toolengagement means such that said fastener is selectively installed in aworkpiece by engagement of said tool means with said tool engagementmeans and operation. of said tool means.
 26. The installation tool ofclaim 24 wherein said fastener is installed by rotation of the fastenerrelative to said workpiece, said tool means imparting rotational motionto said tool engagement means for installation of said fasteners. 27.The installation tool of claim 26 the load measuring device of claim 13wherein said measurement means provides an output signal indicative ofthe elongation of said shank and further wherein said load measuringdevice further comprises:commutator means for communicating said outputsignal to said wrenching means.